1. Field of the Invention
The present invention relates to a photosensitive polymer and a photoresist composition thereof.
2. Description of the Related Art
A smaller sized pattern design rule of not greater than 0.2 xcexcm is necessary in a semiconductor memory device having a capacity exceeding 1 Gbit. A photolithographic technique has been proposed in which an argon fluoride excimer laser (xe2x80x9cArFxe2x80x9d) capable of forming 0.1 xcexcm patterns and having a wavelength of 193 nm, which is even shorter than that of a conventional krypton fluoride excimer laser (xe2x80x9cKrFxe2x80x9d) having a wavelength of 248 nm, and a F2 excimer laser capable of forming 0.07 xcexcm patterns and having a wavelength of 157 nm, are used as a new type of exposure light source. According to the change in exposure light source, there is an increasing demand for developing new photoresist materials having transparency at a shorter wavelength of 193 nm or less; high resistance to dry etching; good adhesion to layer materials above or below; easily capable of being developed using conventional aqueous developing solutions; and excellent in annealing effect during baking.
However, compared to the conventional KrF resist materials, known ArF or F2 resist materials pose many problems for practical use. For example, poly(methyl methacrylate-t-butyl methacrylate-methacrylic acid), a terpolymer known in the art, is weak in resistance to dry etching.
In the case of a cycloolefin-maleic anhydride (xe2x80x9cCOMAxe2x80x9d) alternating polymer having the following formula, the production cost of raw material is cheap, whereas yield of the polymer sharply decreases. In addition, the transmittance of the polymer is very low at a short wavelength region, such as, for example, at 193 nm. The above COMA synthetic polymers have alicyclic hydrocarbon in their backbone, which shows prominent hydrophobicity, and thus the adhesiveness to neighboring material layers below is very poor. 
The copolymer has a glass transition temperature of 200xc2x0 C. or more due to the structural characteristic of the backbone. As a result, it is difficult to achieve an annealing effect for eliminating a dynamic volume from the resist layer formed of the polymer with the above structure during baking. Accordingly, the resist layer has poor environmental resistance. As a result, when the polymer contacts a basic contaminant in the atmosphere, acid (xe2x80x9cH+xe2x80x9d) generated from a photoacid generator (xe2x80x9cPAGxe2x80x9d) by exposure cannot participate in acidolysis in the polymer and is quenched. Also, the acid is easily diffused into a non-exposed portion, thereby producing a photoresist pattern having a poor profile, such as, for example, a T-top profile. In addition, the resist layer is deformed due to e-beam while the photoresist pattern is observed by V-SEM, thus making it difficult to determine a good or bad state of the pattern. Also, these polymers do not have satisfactory transmittance.
The above and other drawbacks and disadvantages of the prior art are addressed by embodiments of the present disclosure that provide a photosensitive polymer which has a high enough glass transition temperature to acquire an annealing effect during baking while satisfying requirements as a main component of a resist material.
It is another advantage of the present invention to provide a photoresist composition containing the photosensitive polymer, suitable for an exposure light source having a shorter wavelength of 193 nm or less.
Accordingly, to achieve the above advantage, there is provided a photosensitive polymer including 10 to 90 mol % of an alkyl vinyl ether monomer having the formula, and 10 to 90 mol % of at least one monomer selected from the group consisting of an acrylate derivative, methacrylate derivative, fumarate derivative and 4-hydroxy styrene derivative, having an acid-labile hydrocarbon with from 4 to 20 carbon atoms, or at least one monomer selected from the group consisting of acrylonitrilie derivative and norbornene derivative, having an acid-labile substituent group with from 4 to 20 carbon atoms, and the photosensitive polymer has a weight average molecular weight of 3,000 to 50,000: 
where x is an integer from 3 to 6 inclusive, R1 and R2 are independently alkyl having from 1 to 20 carbon atoms, fluorinated alkyl having from 1 to 10 carbon atoms or perfluoronated alkyl having from 1 to 10 carbon atoms.
In another aspect of the present invention, a photosensitive polymer includes 10 to 90 mol % of an alkyl vinyl ether monomer having the formula, and not greater than 50 mol % of a maleic acid anhydride monomer, wherein the photosensitive polymer has a weight average molecular weight of 3,000 to 50,000.
Preferably, the photosensitive polymer further includes at least one monomer selected from the group consisting of an acrylate derivative, methacrylate derivative, fumarate derivative and 4-hydroxy styrene derivative, having an acid-labile hydrocarbon with from 4 to 20 carbon atoms, or at least one monomer selected from the group consisting of acrylonitrilie derivative and norbornene derivative, having an acid-labile substituent group with from 4 to 20 carbon atoms.
According to another aspect of the present invention, there is provided a photoresist composition including at least one polymer selected from the above photosensitive polymers, and 1.0 to 15 wt % of a photoacid generator (xe2x80x9cPAGxe2x80x9d) based on the weight of the photosensitive polymer.
Preferably, the PAG includes a triarylsulfonium salt, diaryliodonium salt, sulfonate or a mixture of these materials.
The resist composition may include 0.01 to 20 wt % by weight an organic base based on the weight of the photosensitive polymer.
A photosensitive polymer and a photoresist composition thereof are provided and described. Also, a preferred photolithography process using the photoresist composition will be described. This invention may, however, be embodied in many different forms, and these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In formulas, the same characters denote the same functional groups.
A photosensitive polymer according to an exemplary embodiment of the present disclosure includes 10 to 90% by mole of a hydroxy alkyl vinyl ether monomer, and thus has vinyl ether as a main component of its backbone. The vinyl ether backbone is more flexible than a conventional alicyclic hydrocarbon backbone, contributing to lowering a glass transition temperature of the photosensitive polymer. The vinyl ether is preferably substituted by a C1-C20 hydroxy alkyl group to further increase the flexibility of the photosensitive polymer. More preferably, the vinyl ether is substituted by a C1-C10 hydroxy fluoroalkyl group or a C1-C10 hydroxy perfluoroalkyl group to increase transmittance with respect to an exposure light source of 157 nm. Since the substituent includes a hydroxy group (xe2x80x94OH), the adhesion and wettability of the photosensitive polymer against layer materials can be enhanced. The vinyl ether monomer can be expressed by the following formula 2:
wherein x is an integer in the range of 3 to 6 inclusive, R1 and R2 are individually C1 to C20 alkyl, C1 to C10 fluoronated alkyl or C1 to C10 perfluoronated alkyl.
Since the hydroxy alkyl vinyl ether monomer has an electron-donating property, it is polymerized with one or more other monomers having an electron-withdrawing property to facilitate polymerization, thereby forming a photosensitive polymer. Usable monomers capable of being polymerized with the hydroxy alkyl vinyl ether monomer include monomers selected from the group consisting of an acrylate derivative, methacrylate derivative, fumarate derivative and 4-hydroxy styrene derivative, having an acid-labile hydrocarbon with from 4 to 20 carbon atoms, or monomers selected from the group consisting of acrylonitrilie derivative and norbornene derivative, having an acid-labile substituent group with from 4 to 20 carbon atoms. The electron-withdrawing monomer is included in the polymer in a ratio of 10 to 90% by mole.
For acrylate derivatives, methacrylate derivatives, fumarate derivatives or 4-hydroxy styrene derivatives, t-butyl, tetrahydropyranyl or 1-ethoxy ethyl is suitably used as the C4 to C20 acid-labile hydrocarbon group.
In the case where the acid-labile substituent group is a C6 to C20 alicyclic hydrocarbon group, the dry etching resistance of the photosensitive polymer is improved.
For acrylonitrile derivatives or norbornene derivatives, a C4 to C10 ester group is suitably used as the acid-labile substituent group.
The monomers can be polymerized by general radical polymerization, cationic polymerization or anionic polymerization. The polymerized photosensitive polymers have an appropriate weight average molecular weight of 3,000 to 50,000.
Examples of copolymers suitable for the photosensitive polymers according to exemplary embodiments of the present disclosure are represented by the following formulas 3 and 4, and examples of terpolymers suitable for the photosensitive polymers according to exemplary embodiments of the present disclosure are represented by the following formula 5: 
wherein m and n are both integers, the value of m/(m+n) differs according to the kind of alkyl vinyl ether monomer used, preferably in the range of 0.1 to 0.9 from the viewpoint of adjustment of overall characteristics; 
wherein m and n are both integers, and m/(m+n) equals 0.1 to 0.9; and 
wherein m, p and q are all integers, and m/(m+n+q) equals 0.1 to 0.4, n/(m+n+q) equals 0.1 to 0.5, and q/(m+n+q) equals 0.1 to 0.5.
In formulas 3-5, wherein R3 hydrogen or methyl; R4 is C4 to C20 acid-labile hydrocarbon; and R5 is C4 to C20 acid-labile substituent group. R4 is preferably t-butyl, tetrahydropyranyl or 1-ethoxy ethyl, facilitating the photosensitive copolymer to function as a positive chemically amplified resist.
Also, R4 may be C6 to C20 tertiary alicyclic hydrocarbon. Suitable tertiary alicyclic hydrocarbons include 2-methyl-2-norbornyl, 2-ethyl-2-norbornyl, 2-methyl-2-isobornyl, 2-ethyl-2-isobornyl, 8-methyl-8-tricyclo[5.2.1.02,6]decanyl, 8-ethyl-8-tricyclo [5.2.1.02,6]decanyl, 2-methyl-2-adamantyl, 2-ethyl-2-adamantyl, 2-propyl-2-adamantyl, 2-methyl-2-fenchyl and 2-ethyl-2-fenchyl. Use of the tertiary alicyclic hydrocarbons increases dry etching resistance of the photosensitive polymer.
In the copolymer represented by the formula 3, since a first monomer is hydroxy alkyl vinyl ether and a second monomer is an acrylate derivative or methacrylate derivative, the backbone of the polymer is very flexible. Thus, the glass transition temperature of the photosensitive polymer has an appropriate value in the range of approximately 130 to approximately 180xc2x0 C.
In formula 4, R5 is preferably an acid-labile ester for the photosensitive polymer to function as a positive chemically amplified resist.
The acid-labile ester is preferably t-butyl ester, tetrahydropyranyl ester or 1-ethoxyethyl ester.
In formulas 4 and 5, norbornene used in the backbone increases the dry etching resistance.
In another exemplary embodiment of the present disclosure, there is provided a photosensitive polymer including at least 10 to 90 mol % of a hydroxy alkyl vinyl ether monomer and not greater than 50 mol % of an maleic acid anhydride monomer. In this case, a copolymer having the formula 6, a terpolymer having the formula 7 or 8, or a tetrapolymer having the formula 9, is suitably used as the photosensitive polymer according to alternate embodiments of the present disclosure. R1 through R5 are as defined above. 
wherein m, n and q are all integers, and m/(m+n+q) equals 0.1 to 0.4, n/(m+n+q) equals 0.1. to 0.5, and q/(m+n+q) equals 0.1 to 0.5. 
wherein m, n and p are all integers, and m/(m+n+p) equals 0.1 to 0.4, n/(m+n+p) equals 0.1 to 0.5, and q/(m+n+p) equals 0.1 to 0.5. 
wherein m, n, p and q are all integers, and m/(m+n+p+q) equals 0.1 to 0.4, n/(m+n+p+q) equals 0.1 to 0.5, and p/(m+n+p+q) equals to 0.1 to 0.4 and q/(m+n+p+q) equals 0.1 to 0.5.
If a monomer of maleic acid anhydride is further included, a more perfect alternating copolymer can be obtained by general radical polymerization. Therefore, the yield of polymers can be increased.
To prepare a photoresist composition according to exemplary embodiments of the present disclosure, the polymers synthesized above are dissolved in various types of solvents such as propylene glycol monomethyl ether acetate (xe2x80x9cPGMEAxe2x80x9d), ethyl lactate or cyclohexanone with a photoacid generator (xe2x80x9cPAGxe2x80x9d) to prepare a resist solution.
The PAG is preferably contained in an amount of 1 to 15% by weight based on the weight of the photosensitive polymer. Suitable PAGs include triarylsulfonium salts, diaryliodonium salts, sulfonate, N-hydroxysuccinimide triflate or mixtures thereof.
Examples of the PAG include triphenylsulfonium triflate, triphenylsulfonium antimonate, diphenyliodonium triflate, diphenyliodonium antimonate, methoxydiphenyliodonium triflate, di-t-butyldiphenyliodonium triflate, 2,6-dinitro benzyl sulfonate, pyrogallol tris(alkyl-sulfonate), norbornene-dicarboximide triflate, triphenylsulfonium nonaflate, diphenyliodonium nonaflate, methoxydiphenyliodonium nonaflate, di-t-butyldiphenyliodonium nonaflate, N-hydroxysuccinimide nonaflate, norbornene dicarboximide nonaflate, triphenylsulfonium perfluorooctanesulfonate, diphenyliodonium perfluorooctanesulfonate, methoxydiphenyliodonium perfluorooctane sulfonate, di-t-butyldiphenyliodonium triflate, N-hydroxysuccinimide perfluorooctanesulfonate, or norbornene dicarboximide perfluorooctanesulfonate.
Preferably, the photoresist composition of preferred embodiments of the present disclosure further includes 0.01 to 2% by weight of an organic base based on the weight of the photosensitive polymer. Suitable organic bases include tertiary amines. Usable examples of the organic base include triethylamine, triisobutylamine, triisooctylamine, diethanolamine, triethanolamine or a mixture thereof. The organic base is added for preventing a pattern deformation, which results from an unexpected acidolysis caused by the acid generated at the exposed regions and then diffused into the unexposed regions after exposure.
Also, a photoresist composition according to embodiments of the present disclosure includes 30 to 200 ppm of an organic or base surfactant, which functions to allow the photoresist composition to be uniformly coated on a substrate.
To adjust the overall dissolution speed of the resist, the resist composition of exemplary embodiments further includes 5 to 25% by weight of a dissolution inhibitor, based on the weight of the photosensitive polymer.
For a lithography process, the resist solution is first filtered twice using a 0.2 xcexcm membrane filter to thus obtain a resist composition.
The obtained resist composition is subjected to the following process to obtain a pattern.
A bare silicon wafer or a silicon wafer having a layer to be patterned thereon is prepared and treated with hexamethyidisilazane (xe2x80x9cHMDSxe2x80x9d). Thereafter, the silicon wafer layer is coated with the resist composition to a thickness of approximately 0.2 to 0.7 xcexcm to form a resist layer.
The silicon wafer having the resist layer is pre-baked at a temperature in the range of 90 to 180xc2x0 C., preferably 110 to 140xc2x0 C., for approximately 60 to 120 seconds to remove a solvent, followed by exposure using various exposure light sources, for example, a KrF, ArF or F2 excimer laser. In the case of using a light source having a wavelength of 193 nm or less, exposure is performed at a dose of 5 to 100 mJ/cm2. Next, post-exposure baking (xe2x80x9cPEBxe2x80x9d) is performed at a temperature in the range of 90 to 180xc2x0 C., preferably 110 to 140xc2x0 C., for approximately 60 to 120 seconds to cause acidolysis at an exposed portion of a resist layer. As a result, acidolysis actively occurs at the exposed portion, allowing the exposed portion to exhibit very high solubility to a developing solution including 2.38 wt % tetramethylammonium hydroxide (xe2x80x9cTMAHxe2x80x9d). Thus, during development, the exposed portion is dissolved well for removal.
The silicon wafer or the layer to be patterned is etched by a special etching gas, such as plasma, e.g., a halogen or CxFy gas, using the resultant resist pattern as a mask. Subsequently, the resist pattern remaining on the wafer is removed by ashing and a wet process using a stripper, thereby forming a desired pattern.
The resist composition according to embodiments of the present disclosure can solve both problems of transmittance and adhesion associated with conventional resist materials having a COMA polymer as a main component.
Since conventional COMA alternating polymers have a very high glass transition temperature of 200xc2x0 C. or higher due to their rigid backbone, many problems may have been involved during process. On the other hand, the photosensitive polymer included in the resist composition according to exemplary embodiments has an appropriate glass transition temperature in the range of 130 to 180xc2x0 C. Thus, the resist layer formed of the photosensitive polymer according to embodiments of the present disclosure has a sufficient annealing effect during baking, thereby reducing its dynamic volume. Accordingly, the environmental resistance of the resist layer improves, thereby enhancing lithography performance.
Illustrative exemplary embodiments of the present disclosure will be described in detail with reference to the following examples and synthesis examples, and what can be technically deduced by one skilled in the art is not described herein. It is noted that reagents used for explaining the invention are generally available, and most are available from Aldrich Chemical Co.